1. Field of the Invention
The present invention relates to an intake duct for a supercharger and, more particularly, to an air intake duct that fluid connects between a suction port of the supercharger and an outlet port of an air intake control valve.
2. Description of Related Art
In the motorcycle equipped with a supercharger, it is quite often that in order to reduce the mechanical loss, an air intake control valve for adjusting the amount flow of air to be introduced into the supercharger is disposed at a location upstream of the supercharger with respect to the direction of flow of the air. In such case, the air intake control valve is generally so disposed that a valve shaft or valve stem of such air intake control valve may lie perpendicular to a shaft center of the supercharger. By way of example, the valve shaft of the air intake control valve is disposed horizontally and the shaft axis of the supercharger is disposed parallel to a rotary shaft of a motorcycle combustion engine.
Accordingly, if in order to save the space around the combustion engine the air intake control valve is disposed above or below the supercharger, the angle depicted between an axis of an outlet of the air intake control valve and an axis of the inlet of the supercharger will form an angle of substantially 90°. As a result thereof, a tubing or a piping fluid connecting between the both will be curved at an angle of substantially 90° and, accordingly, detachment of the air flowing within this piping will occur on an inner side of the piping so curved, accompanied by generation of noises attributable to the air flow. In view of this, suggestion has been made to use a projection inside such a 90° curved portion of the piping so that the flow of the air can be disturbed to uniformize the velocity distribution of the air flow. In this respect, see the patent document 1 listed below.